Nitrox diving

Nitrox Diving 101: What is Enriched Air Diving?

For most divers, Nitrox diving is the first taste of diving with exotic gasses, and opens up a world of longer, safer dives

Nitrox is the common name used for breathing gasses with a higher percentage of oxygen than in normal atmospheric air.

Actually Nitrox is somewhat of a misnomer as it’s an abbreviation of Nitrogen and Oxygen, which are the main components of both atmospheric air and Nitrox. The proper term for the gas is Enriched Air Nitrox (EANx), pointing to the extra oxygen that the mix is enriched with.

The good of Diving Nitrox

The reason for diving with Nitrox is to use the added oxygen to push out some of the nitrogen in the atmospheric air. Lowering the amount of nitrogen in the mix, and though that, the amount of nitrogen our tissues absorb during the dive.

This in turn reduces the risk of decompression illness and allows for longer bottom times.

For repetitive dives, the nitrogen load carried from one dive to the next is lower than with atmospheric air, again decreasing the risk of decompression illness.

Many divers also report feeling more alert, and less tired after diving with Nitrox.

The bad of diving Nitrox

Scuba Diver using Nitrox on a dive

Torben Lonne – DIVE.in

However, there is a downside. Oxygen is actually toxic for the human body, if breathed under pressure.

How much pressure depends on the oxygen content of the gas mix breathed.

100 % oxygen becomes toxic at only 20 feet or so. The less oxygen in a mix (the more “lean” it is) the deeper you can go before it becomes toxic.

As the first symptoms of oxygen toxicity are violent convulsions, followed by powerful inhalations and loss of consciousness, it can be fatal during a dive.

What is the Enriched Air Nitrox Partial Pressure

Oxygen toxicity happens when the oxygen reaches a critical level of what is known as partial pressure.

Partial pressure is the pressure of any given gas in a mix and the recommended partial pressure for oxygen is 1.4, with 1.6 used as a margin of safety.

As Nitrox comes in varying mixes, the partial pressure of 1.4 is reached at varying depths, depending on the mix.

Therefore, one of the things a Nitrox course teaches you is to measure the mix in your tank and calculate the maximum safe depth it can be used on.

The Different Nitrox mixes

Nitrox Scuba Tanks being filled at a Filling Station

Royster

The most common mixes used are EANx32 and EANx36, with 32 % and 36 % oxygen, respectively, compared to 21 % oxygen in atmospheric air.

Other mixes are also used, but mixes richer than 40 % are rare in recreational diving. For a dive shop to cater to Nitrox divers, they need to specifically certify to mix Nitrox gasses.

Maximum Depths with Nitrox

Needless to say, once you’ve measured the mix in your tank, which is done with an O2 meter and you have calculated the maximum safe depth that mix can be used at, it is imperative that you stay above that depth.

Keeping a close watch on your depth gauge is critical, especially in situations where the maximum possible depth of the dive exceeds your mix’s maximum depth such as wall dives.

Most modern dive computers allow you to set a depth alarm, where it will give you an audible warning when a certain depth is reached. This is highly recommended if you dive with Nitrox.

Diving Nitrox with your Dive Computer

Some dive computers have a Nitrox setting built in to them. These come in two versions, either where the dive computer has a selection of preset mixes that you can chose from. Or where you enter the mix yourself and the computer subsequently determines maximum depth and dive time based on that. The latter is typically found in more advanced computers.

If your computer has presets, and your mix doesn’t match any of them exactly. The general advice is to always err on the side of caution and round up, not down, especially for deeper dives.

Scuba diving computer

Nart

Say your computer has presets for Nitrox mixes of 32 %, 34 %, and 36 %, yet the mix in your tank reads as 33 % when you measure it on the O2 meter. In that case, set your dive computer to the preset for 34 %, which will reduce your depth compared to the mix you actually have, allowing for a margin of safety.

If, however, your dive is a particularly long one, where you’ll be coming up on the maximum dive time of your mix, and with little or no risk of exceeding the depth limit (say you’re diving in an area where the bottom is quite a bit shallower than your maximum depth). It’s safer to set the preset to 32 %, which will reduce your maximum bottom time, again, giving you a margin of safety.

Always know what you’re doing

Nitrox diving is for many the first taste of non-atmospheric gasses, and with that, an early intro to technical diving.

For this reason, it should be taken seriously and no diver should attempt diving with Nitrox without having taken a Nitrox course with an accredited dive center.

With this certification, though, diving can become safer and more enjoyable.

Have you tried Nitrox?

Have you ever tried diving with Enriched Air Nitrox before? Tell us about your first “almost tech” diving experience.

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Thomas Grønfeldt Senger

Thomas is a Naui Instructor and has been diving in Australia, France, Egypt, Sweden, Indonesia, Iceland, and numerous other locations around the world.
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There are 2 comments

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  1. Craig

    Started diving Nitrox 2 years ago. I am 62 years old and it allows me to do 4 dives a day and maintain my alertness and minimal fatique. It also allows for shorter wait times between dives hence 4 is quite doable. Nitrox is a good way to dive for us seniors. I am certified advanced and certified nitrox and it makes you think when gearing up as you have to check the O2 level in the tank as well as set your computer and make sure you know what depth is your max.

  2. jim olinger

    I earned my nitrox card in Bonaire. It was a great place to start using it as you can easily do 4 tanks / day there and greatly reduce the nitrogen loading.
    That puts to me to thinking of the instructor for the course. Here name was “F” and she was from Italy and stunningly attractive! She was on the boat for my first nitrox dive and after surfacing she said, “So tell me Jim, do you feel “jounger?” Do you feel “strongger”? There are rumors of this you know?”
    I glanced over at my wife and realized I was in VERY dangerous waters!
    “yes, it was a great dive!” I replied with a big grin on my face.
    So I’m not sure if it was “F’s” statement or something more physiological, but I did in fact feel a bit better…almost refreshed with the enriched O2 content.


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